Purification of benzene



United States PatentO' PURIFICATION OF BENZENE Ernest Carlton Housam and Ronald Lester, Sunbury-on- Thames, England, assignors to The British Petroleum Company Limited, London, England, a British joint. stock corporation No Drawing. Filed July 9, 1957, Ser. No. 670,666

Claims" priority, application GreatBritain July 11, 1956 5 Claims. (Cl. 260-674) This invention relates to the purification of benzene,

and particularly to the production of nitration grade benzene.

It is well known that. itis diflicult. to separate benzene from non-aromatic hydrocarbons by simple fractional distillation owinglto the formation of azeotropes. It is particularly a problem in the production of nitrationgrade benzene from certain crude benzoles, since these latter contain a proportion of paraflins and naphthenes which are not separable. by simple fractional distillation. In consequence the product fails to pass the stringent requirements of crystallisation point and specific gravity set down for nitration grade benzene. In addition'nitra tion grade benzene must satisfy other requirements snchflf as distillation range, carbon disulphide and thiophene content. Full details of the nitration grade. benzene..3 specification are given in British Standard Specification: 135:1953, Benzoles.

According to the present invention benzene is sep- 7 arated from mixtures of benzene andnon-aromatic hydrocarbons which form azeotropes with the benzene by subjecting the mixture to catalytic reforming and fractionally distilling the reformed product to obtain a ben-f zene fraction. understood to mean a fraction rich in benzene "but not excluding minor proportions of other. hydrocarbons. The preferred benzene fraction is one passing the nitration f grade benzene specification.

The catalytic reforming step converts part of the nonv aromatic hydrocarbon content to additional benzene and the remainder to compounds from which'benzene can be separated by simple fractional distillation. As mentioned. above, the process is applicable to the production of nitration grade benzene from crude benzole, for example gas works benzole. Such benzoles also contain sulphur and nitrogen compoundsso .that these and other sulphur, containing feedstocks require desulphurising in addition to reforming.

This desulphurisation is preferably carried outsimultaneously with the reforming in a single-stage catalytic refo'rmingand hydrodesulphurisation treatment, by. selecting a sulphur-resistant catalyst having bothreforming and' desulphurising properties, for example a catalyst containing the oxides of cobalt and molybdenum (either as such'or as cobalt molybdate or both) supported on alumina.

desulphurised or acid treated prior to the catalytic 'reforming in which case the reforming catalyst need not be sulphur-'re'sistant-At aybe for example a'catalystof The conditions for the catalytic reforming; whether 'drofined under the following'operating conditions. readily apparent that the crude benzole contained a major u a The term benzene fractlon to be but this fheartcut was found to have a specific gravity Alternatively the feedstock'may be hydro- 60 as follows: r

. 2' t with simultaneous hydrodesulphurisationor' not, are preferably selected from the following ranges:

: hydrocarbon ratio.

The precise operating conditions used will depend on the characteristics of the feedstock, for example the relative proportion of non-aromatic hydrocarbons to benzene and experiments may be necessary tode't'erminc, the optirnum operating conditions for any given feedstock. v g V The subsequent fractional distillation should: rep; erably be such as to obtain a narrow benzene heart out,

particularly if nitration grade benzene is required.

The invention is illustratedbythe following examples. 1 1

Example 1 A Barbet benzene, that is a distillate from gas works crude benzole containing over of benzene, was hy-- It is p a ct nar ,7

below the limits specified for nitration grade benzene (,0.8830.'886). The inspection data were:

. Total Hydrofined Feedstock hydrofined .benzene.

V product heart cuti Specific gravity,'60 F./60 F 0.8785 0.8730 0.8780, Sulphur, percent wt 0. 424 0.005 0. 0002;

This benzene heart out was then"'catalyti allyzIre: I formed under theffollowing.conditionsa.

Space velocity l.0.v./v./hr. 5 Gas rate 1/1 mol' H /hydrocarbon.

ratio. s

'The. resulting 'reformate was distilledg in a,-2l0-plate column ata reflux ratio. of 20:1 to gi eJa-benzene'heam cut. This cut met alltherequirementsj. of the. National Benzole Association nitration; gradebenzenerspecificap Test Nltration grade benzene speei- Catalytically reformed ficatiou benzene heart out Specific gravity at 15.5 0./15.5 O 0883-0886 0.8835.

Dlstillatio IBP The difference between the 5% volume and the 97% volume temperatures shall not exceed 0.4" O. This range shall be between 705 C and 805 C.

Sulphur as carbon disulphide. N at more than 0.035 0.003.

Sulphur as thiophene ..1 Not more than 0.01 0.00025.

crystallisation point O Not below 5.0 5.3.

Residue on evaporatiommg. /100 m1. Not greater than 5 3.

Water Free from undissolved water Free from undissolved and other separated impuriwater and other ties at 15.5 C. iseparated impurties.

Acid wash test Palcr than a standard solution Paler than standard.

Colour do Do.

HQS and mercaptans. Negative to doctor test." "1 Negative.

Neutrality Must not give an acid reaction Neutral.

with the National Benzole Association mixed indicator.

Example 2 Association specification for nitration grade benzene are A Barbet benzene, that is a distillate from gas works 30 Set out in The following table- Feed- Total Reformed benzene heart out T st stock reformed (N BA specn. tests) N itratlon grade benzene specification product Specific gravity at 155 C./15.5 O 0. 8785 0. 8695 0.8835"... 0883-0886.

Distillation:

P 2% vol. 5% volvolvol 28g '8; The difference between the 5% volume 9 and the 97% volume temperatures shall not exceed 0.3" C. This r ange shall be vol between 79.5 C. and 80.5 C. vol vol vol 97% vol FB P Recovery" Residue.

s Total sulph Sulphur as carbon disulphide. N ot more than 0.035. Sulphur as thiopheue Not more than 0.01. Crystallization point. N at below 5.0. Residue on evaporation Not greater than 5. Water Free from undissolved water and other separated impurities. separated impurities at 15.5 0. Acid wash test Palcr than standard.. Palcr than a standard solution. Colour do Do. His and mereaptans- Doctor ne at ve" Negative to doctor test. Neutrality Slightly alkaline Must not give an acid reaction with the National Benzole Association mixed indicator.

crude benzole containing over 90% of benzene, was

treated under the following operation conditions:

Pressure 700 p.s.i.g. Temperature 940 F.

Space velocity 0.5 v./v./hr, Gas rate 4000 s.c.f./b. Make-up gas Pure hydrogen.

It will be seen that the heart out from the reformed and desulphur'ised product met all the requirements for nitration grade benzene.

We claim: 1.' In a method of separating benzene from crude benzole mixtures comprising benzene and non-aromatic hydrocarbons which form azeotropes with the benzene, and sulphur compounds, said mixtures containing a major portion of benzene, and said method including the step of desulphurising the mixture, the improvement which comprises subjecting the mixture to catalytic reforming by contacting the mixture in the presence of added hydrogen with a reforming catalyst at a pressure in the range of 50 to 100 p.s.i.g;, a temperature in the range of from '850" F. to 1050 R, a space velocity in the range of from 0.5 to 5 v./v./hr. and a molar hydrogen/hydrocar- 75 'bon ratio in the range of from 0.5:1 to 15:1, and fracall ege'iasse id 0 tionally distilling the reformed desulphurised product to obtain a benzene fraction.

2. -A method as claimed in claim 1, wherein the mixture is simultaneously catalytically reformed and bydrodesulphurised by the use of a sulphur-resistant catalyst having both reforming and desulphurising properties.

3. A method as claimed in claim 2, wherein the catalyst comprises the oxides of cobalt and molybdenum supported on alumina.

4. A method as claimed in claim 1, wherein the mixture is treated prior to the catalytic reforming to desulphurise it.

5. The method of claim 4 wherein the catalytic reform- 6 ing of the desulphurised mixture is carried out in the presence of a catalyst of platinum supported on alumina.

References Cited in the file of this patent UNITED STATES PATENTS Great Britain Jan. 19, 1955 UNITED STATES PATENT OFFICE I CERTIFICATION OF CORRECTIQN P' atent. No. 2,976,336 March 21, 1961 Ernest Carlton Housam et al.

It is hereby certified that error eppears in the above numbered patent requiring correction and that the said Letters Patent should read as corrected below.

Column 4, line 72 for '100'r. read 1000 Signed and sealed this 22nd day of August 1961.

(SEAIBE Attest: ERNEST W SWIDER I 7 DAVID L. Attestihg Officer Commissioner of Patents 

1. IN A METHOD OF SEPARATING BENZENE FROM CRUDE BENZOLE MIXTURES COMPRISING BENZENE AND NON-AROMATIC HYDROCARBONS WHICH FORM AZEOTROPES WITH THE BENZENE, AND SULPHUR COMPOUNDS, SAID MIXTURES CONTAINING A MAJOR PORTION OF BENZENE, AND SAID METHOD INCLUDING THE STEP OF DESULPHURISHING THE MIXTURE, THE IMPROVEMENT WHICH COMPRISES SUBJECTING THE MIXTURE TO CATALYTIC REFORMING BY CONTACTING THE MIXTURE IN THE PRESENCE OF ADDED HYDROGEN WITH A REFORMING CATALYST AT A PRESSURE IN THE RANGE OF 50 TO 100* P.S.I.G., A TEMPERATURE IN THE RANGE OF FROM 850*F. TO 1050*F., A SPACE VELOCITY IN THE RANGE OF FROM 0.5 TO 5 V./V./HR. AND A MOLAR HYDROGEN/HYDROCARBON RATIO IN THE RANGE OF FROM 0.5:1 TO 15:1, AND FRACTIONALLY DISTILLING THE REFORMED DESULPHURISED PRODUCT TO OBTAIN A BENZENE FRACTION. 